Musnad Ahmad 30:1418

'Affan narrated to us, Hammad narrated to us, Thabit informed us, from Abu Rafi', from Abu Hurairah, that the Messenger of Allah, peace and blessings of Allah be upon him, said: "The angels of the night and the angels of the day gather at the dawn prayer and the afternoon prayer. When the angels of the day ascend, Allah, the Mighty and Majestic, says to them: 'Where have you come from?' They say: 'We came to You from Your servants; we came to them while they were praying, and we came to You while they were praying.' When the angels of the night ascend, Allah, the Mighty and Majestic, says to them: 'Where have you come from?' They say: 'We came to You from Your servants; we came to them while they were praying, and we came to You while they were praying.'"